1. Field of the Invention
The present invention relates generally to mass storage device control structures and methods and more specifically to structures and methods within the controller of a mass storage device, such as a disk drive, operable to map all logical block addresses to corresponding physical block addresses so as to provide independence of the logical block size and physical block size. The same mapping also enables sequential writing of concentric cylinders of the storage device thereby enabling numerous other benefits including use of a physically wider write head.
2. Discussion of Related Art
A common example of a mass storage device is a disk drive having one or more rotating recordable media surfaces each with a corresponding read/write head for writing information thereon and for reading back previously written information. As used herein, “disk drive” is intended to represent such devices with rotating storage media and corresponding read/write heads as well as other similar, exemplary mass storage devices. Further, “recordable media”, “recordable media surface”, “persistent media” are all intended as synonymous and represent one or more media surfaces on this information may be recorded and read back—typically using optical or magnetic encoding and modulation techniques and structures.
It is generally known in the disk drive arts that fixed sized units of data are physically stored about the circumference of concentric tracks laid out on a magnetic or optical persistent storage medium. These fixed size units of data are often referred to as “blocks” or “sectors”. A particular block or sector physically located on the rotating storage medium may be identified by its cylinder or track number and its sector or block number within that track. In addition, where a disk drive includes multiple storage media services each with an independent read write head, a particular head or surface number may identify the surface on which a particular physical block or sector is located. Such physical addresses are often referred to as “CHS” (an acronym for cylinder, head, sector).
Most present-day disk drives permit a logical block address to be utilized by the host system or device rather than a specific CHS designation to identify a particular block or sector to be accessed. Such a logical address is typically a sequential range of logical block numbers from zero through N where N is the maximum number of physical sectors or blocks available on the disk drive storage media. The host may therefore address or identify a particular physical block by its logical block address (“LBA”) rather than by the more complex and cumbersome CHS designation. The disk drive (specifically a disk drive controller component of the disk drive) then translates or maps a provided logical block address (LBA) into a corresponding physical location (typically, a CHS address designation). Further, such logical addressing permits the disk drive controller to transparently redirect access for a particular physical block to an alternate or spare physical block where the original physical block has been damaged or is otherwise inaccessible. The disk drive controller merely translates the supplied LBA to a different physical block of the disk storage media.
As presently practiced in the art, physical sectors or blocks on the disk drive are all the same size as measured in number of bytes. For example, present disk drives often utilize a block or sector size of either 512 or 1024 bytes. The particular physical block or sector size may be any suitable size selected for a particular disk drive application in accordance with performance and storage capacity design choice tradeoffs. However, as presently known in the art, physical sectors on a disk drive are all a common, designated size. The logical blocks utilized by a host device in addressing storage of the disk drive are also a fixed size. Though the fixed size of a logical block may be different than the fixed size of the physical disk blocks, as presently practiced a simple arithmetic computation may be used because the physical block size and logical block size are typically integral multiples/fractions of one another. In other words, as presently practiced, a logical block size is typically an integral multiple of the physical block or sector size. Such a strict arithmetic relationship between the logical block size and physical block size precludes a number of possible features and enhancements within a disk drive.
Another issue arising in disk drive technology is the track density (i.e., number of concentric tracks or cylinders per inch or “TPI”). The width of the write head portion of the read/write head assembly is a critical factor in this measure of radial track density. A narrower, more costly write head is capable of accurately writing tracks more closely spaced radially while a wider, less costly write head generates tracks that must be more widely spaced radially and hence reduces track density. Since random write operations are normal in traditional mass storage devices (such as disk drives), the width of the write head must be large enough to permit random writing and rewriting of tracks without interfering with adjacent, previously recorded tracks.
It is evident from the above discussion that a need exists for an improved logical to physical mapping for blocks of data within a disk drive of such that the logical block size defined by an attached host system may be independent of the physical block size used within the disk drive for storage of information. It is also evident from the above discussion that an ongoing need exists for a mass storage device (disk drive) capable of maintaining a high radial track density while minimizing the cost of the write head assembly.